In order to determine the impact on
disease resistance of four dietary
immunomodulators viz., beta-1,3
glucan,
levamisole,
vitamins C and E, in an important farmed Indian major carp species, rohu (Labeo rohita Ham.), fish were fed diets containing various levels of these substances during a 60 day trial.
Aflatoxin B1 (AFB,)
at 125 mg kg(-1)
body weight was injected intraperitoneally (i.p.) into fish to induce an immunosuppressive state on the first day of the experiment in some individuals. The fish were vaccinated against
formalin-killed Edwardsiella tarda
vaccine on day 30 of the experiment. Specific immunity, as measured by bacterial agglutination titre and
disease resistance against E. tarda, was determined at the end of the trial. The results demonstrate that all the four
immunomodulators were capable of significantly (P<0.05) increasing specific immunity and reducing mortality in immunocompromised fish but failed to enhance specific immunity and protection in healthy fish. The increased bacterial agglutination titre by beta-1,3
glucan, and reduced mortality losses by both beta-1,3
glucan and
levamisole were marked in healthy vaccinated fish compared with their controls. Similarly, all four substances significantly reduced the mortality rates in immunocompromised and healthy unvaccinated fish. Out of these four substances,
glucan was recorded to be the most effective
immunomodulator in rohu. The present results suggest that the introduction of these substances into the diet of fish grown in farms under immunosuppressive/stressful conditions could increase their resistance to
infection by reducing mortality rates and offer economic benefits.